Phosphine oxide-substituted pyridazine and pyrazine

ABSTRACT

Phosphine oxide of the formula selected from the group consisting of ##STR1## wherein X is H, alkylthio of 1-4 carbon atoms, or ##STR2## Y is H, alkyl of 1-4 carbon atoms, Cl, Br, or ##STR3## Z is H, alkyl of 1-4 carbon atoms, or ##STR4##  at least one of X, Y, and Z in the formula in which all three symbols appear is ##STR5## Q is H or Br; each of A and A&#39; is selected independently from H and alkyl of 1-4 carbon atoms, or A and A&#39; taken jointly is CH═CH--CH═CH; 
     each of D and D&#39; is selected independently from H and CN, or D and D&#39; taken jointly is CH═CH--CH═CH; and 
     each R is selected independently from alkyl of 1-4 carbon atoms, cycloalkyl of 5-6 carbon atoms, benzyl, phenyl, tolyl, and chlorophenyl.

This is a division, of application Ser. No. 049,481, filed June 18,1979, and issued Nov. 18, 1980 as U.S. Pat. No. 4,234,729.

TECHNICAL FIELD

This invention relates to a phosphine oxide-substituted pyridazine,pyrimidine or pyrazine which is useful as a flame retardant forpolymeric materials.

BACKGROUND

Hewertson et al. in J. Chem. Soc., 1963, 1670 disclose the preparationof 2,4,6-tris(dialkoxyphosphinyl)-1,3,5-triazines from cyanuric chlorideand trialkyl phosphites. Also disclosed is the tris(diphenylphosphinyl)derivative which decomposes above 300° C. and hydrolyzes readily tocyanuric acid and diphenylphosphinic acid. The preparation ofbis(diphenylphosphinyl)-1,2,4,5-tetrazine is disclosed by Disteldorf etal. in Ann., 1976, 225. The preparation of various dialkyl 2-, 4- and5-pyrimidylphosphonates is disclosed by Kosolapoff et al. in J. Org.Chem., 26, 1895 (1961).

DISCLOSURE OF INVENTION

For further comprehension of the invention and of the objects andadvantages thereof reference may be made to the following descriptionand to the appended claims in which the various novel features of theinvention are more particularly set forth.

The invention resides in a phosphine oxide which is useful as a flameretardant for polymeric materials. More particularly, the inventionresides in a phosphine oxide wherein each of the one or more phosphorusatoms is bonded to a carbon atom of a pyridazine, pyrimidine or pyrazinenucleus. The phosphine oxide is of the formula selected from the groupconsisting of ##STR6## wherein X is H, alkylthio of 1-4 carbon atoms, or##STR7## Y is H, alkyl of 1-4 carbon atoms, Cl, Br, or ##STR8## Z is H,alkyl of 1-4 carbon atoms, or ##STR9## at least one of X, Y, and Z inthe formula in which all three symbols appear is ##STR10## Q is H or Br;each of A and A' is selected independently from H and alkyl of 1-4carbon atoms, or A and A' taken jointly is CH═CH--CH═CH;

each of D and D' is selected independently from H and CN, or D and D'taken jointly is CH═CH--CH═CH; and

each R is selected independently from alkyl of 1-4 carbon atoms,cycloalkyl of 5-6 carbon atoms, benzyl, phenyl, tolyl, and chlorophenyl.

Examples of operable alkylthio groups in the definition of X includemethylthio, propylthio, and isobutylthio. Examples of operable alkylgroups in the definitions of Y, Z, A, A' and R include methyl, ethyl,isopropyl, butyl, and t-butyl. Because of the availability of startingmaterials, both R groups are preferably the same.

Generally, based on my experience, the best method of preparing thephosphine oxide of the invention, as is illustrated in the exampleswhich follow, is to heat, at reflux temperature, a solution ino-dichlorobenzene of: (1) the methyl or ethyl ester of the appropriatedisubstituted phosphinous acid (that is, the alkyl phosphinite); and (2)the appropriate pyridazine, pyrimidine, or pyrazine containing one ormore chloro substituents in the position or positions into which it isdesired to introduce one or more disubstituted phosphinyl groups. Higheralkyl phosphinites can be used, but the methyl and ethyl esters arepreferred because the by-product methyl chloride and ethyl chloride,respectively, are low-boiling and, therefore, can be easily removed fromthe reaction mixture. Bromo or iodo substituents can be used in place ofthe chloro substituent, but these are less preferred because the bromoand iodo substituted materials are less readily available and theresultant by-products are less volatile. The progress of the reactioncan be followed by noting the evolution of alkyl halide formed as aby-product.

It is anticipated that, in place of o-dichlorobenzene, other solventswould be operable. These include chlorobenzene, toluene, andacetonitrile, but longer reaction times would probably be requiredbecause of the lower boiling points of such solvents in an open system.It is also anticipated that the process would be operable in the absenceof a solvent, but use of a solvent helps moderate the reaction andcontrol the temperature.

Alternatively, the alkyl phosphinite can be formed in situ from thecorresponding dihydrocarbylphosphinous chloride and the appropriatethallium alkoxide, and then reacted, without isolation, with theappropriate pyridazine, pyrimidine or pyrazine. This method isillustrated in Example 10.

The phosphine oxide product of the invention is a colorless or nearlycolorless crystalline solid that is stable to moisture (hydrolysis). Thepreferred phosphine oxide has two or three phosphinyl groups, especiallythe latter, because of its higher phosphorus content, thus imparting agreater flame-retardancy characteristic to the phosphine oxide.

As shown in the following experiments the phosphine oxide product of theinvention is useful as a flame retardant for polymeric materials,particularly polyesters and polyamides. At least a flame-retardingamount, determined for each combination of phosphine oxide and polymerby experimentation, is incorporated in the polymer, either on thesurface or intimately dispersed throughout, preferably the latter. Theprocedure used to evaluate the flame retardancy of the phosphine oxideis described below.

Ten grams of a mixture of powdered polymer and the flame-retardant isthoroughly blended. The mixture is pressed into a film containing aFiberglas® scrim at 5000 lb (2270 kg) ram pressure in a press at anappropriate temperature, about 20°-30° C. above the melting point of thepolymer, and then quenched in ice water. The films thus prepared are cutinto 1.25×3-inch (3.18×7.62-cm) strips and each film is weighed. Thefilm is then held in a U-clamp in a horizontal plane in a vented burnchamber. One exposed edge of the film is ignited for 5 seconds with agas flame 0.75 inch (1.9 cm) high, and the time required for the flamefront to travel from a line 0.5 inch (1.3 cm) from the ignited edge to aline 2.5 inches (6.4 cm) from the ignited edge, or until the flame goesout, is determined. A burn rate, in inches (cm) per minute, iscalculated from the data.

From my experience it has been determined that the burn rate isinversely proportional to the mass of polymer being burned. Therefore,it is necessary to normalize the aforesaid data to a constant polymerweight. This is done by subtracting the scrim weight (constant) from thespecimen weight to obtain the polymer weight and multiplying theaforesaid burn rate by the ratio of the reference polymer weight (noadditive) to the test polymer weight (including additive). Thenormalized rates from a minimum of six specimens of each compositiontested are averaged and compared with data from control samples of thepure polymer to establish the relative effectiveness of the additive onthe burn rate.

The results obtained, using the phosphine oxides of Examples 1, 3, 4 and6, are given in the following table. It may be noted that all the testcompounds lowered the burn rates at low additive levels (2% and 4%),except for the last compound in 66 nylon.

                  TABLE                                                           ______________________________________                                                          Burn rate                                                                     inches/min                                                                    (cm/min)                                                    Product Wt. %               No       With                                     of Ex.  Additive  Polymer*  Additive Additive                                 ______________________________________                                        3       8         2GT       3.00     1.72                                                                 (7.62)   (4.37)                                   4       5         2GT       3.00     2.14                                                                 (7.62)   (5.44)                                   1       5         2GT       3.00     2.51                                                                 (7.62)   (6.38)                                   6       2         2GT       3.00     2.41                                                                 (7.62)   (6.12)                                   6       4         2GT       3.00     2.01                                                                 (7.62)   (5.11)                                   6       5         2GT       3.00     1.88                                                                 (7.62)   (4.78)                                   6       4         4GT       3.30     2.77                                                                 (8.38)   (7.04)                                   6       2         66        1.65     1.65                                                                 (4.19)   (4.19)                                   6       4         66        1.65     1.70**                                                               (4.19)   (4.32)                                   6       5         66        1.65     1.52                                                                 (4.19)   (3.86)                                   ______________________________________                                         *2GT is poly(ethylene terephthalate)                                          4GT is poly(tetramethylene terephthalate)                                     66 is poly(hexamethyleneadipamide)                                            **Flame went out in two of six runs                                      

The following examples illustrate the preparation of the phosphine oxideproduct of the invention. In these examples the products are named asdisubstituted phosphinyl derivatives of pyridazine, pyrimidine, andpyrazine. They can also be named as trisubstituted phosphine oxides.Thus, in Example 1 the product2,3-dicyano-5,6-bis(diphenylphosphinyl)pyrazine can also be named2,3-dicyano-5,6-pyrazinediylbis(diphenylphosphine oxide); in Example 2the product 5-bromo-4-diphenylphosphinyl-2-methylthiopyrimidine can alsobe named 5-bromo-2-methylthio-4-pyrimidinyldiphenylphosphine oxide.

EXAMPLE 1 2,3-Dicyano-5,6-bis(diphenylphosphinyl)pyrazine

To a stirred, refluxing solution of 5.00 g of2,3-dicyano-5,6-dichloropyrazine in 100 ml of o-dichlorobenzene undernitrogen was added dropwise 10.00 g of methyl diphenylphosphinite. Afterthe addition was completed, the mixture was refluxed for 4 hours andthen allowed to stand overnight. The resulting solid was separated byfiltration, washed with benzene and twice with hexane, recrystallizedfrom 200 ml of o-dichlorobenzene, and dried at 80° C./0.1 mm (13 Pa) togive 8.08 g of 2,3-dicyano-5,6-bis(diphenylphosphinyl)pyrazine (shown byformula in claim 4) as a white solid, decomposition beginning at 210° C.Anal. calcd for C₃₀ H₂₀ N₄ O₂ P₂ : C, 67.93; H, 3.80; N, 10.56; P,11.68. Found: C, 67.77; H, 3.92; N, 10.48; P, 11.18.

If ethyl diethylphosphinite is substituted for methyldiphenylphosphinite in substantially the same aforesaid procedure ofthis example, 2,3-dicyano-5,6-bis(diethylphosphinyl)pyrazine will beformed. If methyl di-o-tolylphosphinite is used, the product will be2,3-dicyano-5,6-bis(di-o-tolylphosphinyl)pyrazine.

EXAMPLE 2 5-Bromo-4-diphenylphosphinyl-2-methylthiopyrimidine

To a stirred, refluxing mixture of 3.56 g of5-bromo-4-chloro-2-methylthiopyrimidine in 100 ml of o-dichlorobenzeneunder nitrogen was added dropwise 10.00 g of methyl diphenylphosphinite.After the addition was completed, the mixture was refluxed for 6 hoursand then allowed to cool. Volatiles were removed from the mixture undervacuum, and the residue was recrystallized from 30 ml of 1-chlorobutaneand dried at 50° C./0.1 mm (13 Pa) to give 2.97 g of5-bromo-4-diphenylphosphinyl-2-methylthiopyrimidine as white crystals,mp 124°-127° C. Anal. Calcd for C₁₇ H₁₄ BrN₂ OPS: C, 50.39; H, 3.48; N,6.91. Found: C, 50.54; H, 3.67; N, 6.84.

If 4-chloro-2-ethylthio-6-methylpyrimidine is used in place of5-bromo-4-chloro-2-methylthiopyrimidine in substantially the sameaforesaid procedure of this example,4-diphenylphosphinyl-2-ethylthio-6-methylpyrimidine will be formed. If2-chloropyrimidine is used, the product will be2-diphenylphosphinylpyrimidine.

EXAMPLE 3 4,6-Bis(diphenylphosphinyl)-2-methylthiopyrimidine

To a stirred refluxing solution of 5.00 g of4,6-dichloro-2-methylthiopyrimidine in 150 ml of o-dichlorobenzene undernitrogen was added dropwise 15.00 g of methyl diphenylphosphinite over35 minutes. The mixture was refluxed for 5.5 hours after the additionwas completed and then allowed to cool, at which time it was added to850 ml of n-hexane. The resulting solid was separated by filtration,washed with n-hexane, and recrystallized from 100 ml of ethanol to give11.00 g of 4,6-bis(diphenylphosphinyl)-2-methylthiopyrimidine as whitecrystals, mp 221°-222° C. Anal. Calcd for C₂₉ H₂₄ N₂ O₂ P₂ S: C, 66.15;H, 4.59; N, 5.32. Found: C, 65.59, 65.59; H, 4.54, 4.75; N, 5.04, 5.01.

If methyl ethylmethylphosphinite is used in place of methyldiphenylphosphinite in substantially the same aforesaid procedure ofthis example, 4,6-bis(ethylmethylphosphinyl)-2-methylthiopyrimidine willbe formed. If ethyl dibutylphosphinite is used, the product will be4,6-bis(dibutylphosphinyl)-2-methylthiopyrimidine. If ethylbis(2-chlorophenyl)phosphinite is used, the product will be4,6-bis[bis(2-chlorophenylphosphinyl)]-2-methylthiopyrimidine.

EXAMPLE 4 2,3-Bis(diphenylphosphinyl)quinoxaline

To a stirred, refluxing mixture of 5.00 g of 2,3-dichloroquinoxaline in100 ml of o-dichlorobenzene under nitrogen was added dropwise 14.00 g ofmethyl diphenylphosphinite. The mixture was refluxed for 6 hours afterthe addition was completed and then allowed to stand overnight at roomtemperature. The next day the mixture was admixed with 500 ml ofn-hexane, and the resulting solid was separated by filtration, washedwith hexane, recrystallized from 100 ml of chlorobenzene, and dried at100° C./0.1 mm (13 Pa) to give 9.87 g of2,3-bis(diphenylphosphinyl)quinoxaline (shown by formula in claim 5) asa very slightly yellowish-white solid, mp 258°-272° C. withdecomposition. Anal. Calcd for C₃₂ H₂₄ N₂ O₂ P₂ : C, 72.45; H, 4.56; N,5.28; P, 11.68. Found: C, 72.38; H, 4.23; N, 5.18; P, 11.39.

If 2-chloroquinoxaline is used in place of 2,3-dichloroquinoxaline insubstantially the same aforesaid procedure of this example,2-diphenylphosphinylquinoxaline will be formed. If2-chloro-3-methylquinoxaline is used, the product will be2-diphenylphosphinyl-3-methylquinoxaline.

EXAMPLE 5 4,6-Bis(diphenylphosphinyl)pyrimidine

To a stirred, refluxing mixture of 5.00 g 4,6-dichloropyrimidine in 100ml of o-dichlorobenzene under nitrogen was added dropwise 17.00 g ofmethyl diphenylphosphinite. After the addition was completed, themixture was refluxed for 6.5 hours and then allowed to cool. The cooledmixture was added to 750 ml of n-hexane, and the white solid that formedwas separated by filtration, washed with n-hexane, recrystallized from150 ml of toluene, and dried at 100° C./0.1 mm (13 Pa) to give 13.64 gof 4,6-bis(diphenylphosphinyl)pyrimidine as cream-colored crystals, mp213°-215° C. Anal. Calcd for C₂₈ H₂₂ N₂ O₂ P₂ : C, 70.00; H, 4.62; N,5.83; P, 12.89. Found: C, 69.80; H, 4.65; N, 5.65; P, 12.89.

If 2,4-dichloropyrimidine is used in place of 4,6-dichloropyrimidine insubstantially the same aforesaid procedure of this example, the productwill be 2,4-bis(diphenylphosphinyl)pyrimidine. If2,4-dichloro-6-methylpyrimidine is used, the product will be2,4-bis(diphenylphosphinyl)-6-methylpyrimidine.

EXAMPLE 6 2,4,6-Tris(diphenylphosphinyl)pyrimidine

To a stirred, refluxing mixture of 5.00 g of 2,4,6-trichloropyrimidinein 100 ml of o-dichlorobenzene under nitrogen was added dropwise 26.00 gof methyl diphenylphosphinite. After the addition was completed, themixture was refluxed for 6.5 hours and then allowed to stand overnightat room temperature. The next day a small amount of the solvent wasremoved by boiling, and the solution was allowed to stand againovernight. The next day the resulting solid was separated by filtration,washed twice with benzene and three times with hexane, recrystallizedfrom 650 ml of toluene, and dried at 100° C./0.1 mm (13 Pa) to give11.35 g of 2,4,6-tris(diphenylphosphinyl)pyrimidine as a white solid, mp235°-236° C. Anal. Calcd for C₄₀ H₃₁ N₂ O₃ P₃ : C, 70.59; H, 4.59; N,4.12; P, 13.65. Found: C, 70.72; H, 4.90; N, 3.92; P, 13.61.

If methyl ethylphenylphosphinite is used in place of methyldiphenylphosphinite in substantially the same aforesaid procedure ofthis example, 2,4,6-tris(ethylphenylphosphinyl)pyrimidine will beformed. If ethyl dipropylphosphinite is used, the product will be2,4,6-tris(dipropylphosphinyl)pyrimidine. If methyldiisobutylphosphinite is used,2,4,6-tris(diisobutylphosphinyl)pyrimidine will be formed. If ethyldibenzylphosphinite is used, the product will be2,4,6-tris(dibenzylphosphinyl)pyrimidine.

EXAMPLE 7 1,4-Bis(diphenylphosphinyl)phthalazine

To a stirred, refluxing mixture of 5.00 g of 1,4-dichlorophthalazine in50 ml of o-dichlorobenzene under nitrogen was added dropwise 15.00 g ofmethyl diphenylphosphinite. After the addition was completed, themixture was refluxed for 6 hours and then allowed to stand at roomtemperature for 13 days. The resulting solid was separated byfiltration, washed with benzene and with hexane, recrystallized from 125ml of toluene with decolorizing charcoal treatment, and dried at 100°C./0.1 mm (13 Pa) to give 6.41 g of1,4-bis(diphenylphosphinyl)phthalazine (shown by formula in claim 6) asa light-yellow solid, mp 225°-228.5° C. Anal. Calcd for C₃₂ H₂₄ N₂ O₂ P₂: C, 72.45; H, 4.56; N, 5.28; P, 11.68. Found: C, 72.49; H, 4.62; N,5.36; P, 11.95.

If ethyl bis(4-chlorophenyl)phosphinite is used in place of methyldiphenylphosphinite in substantially the same aforesaid procedure ofthis example, the product will be1,4-bis[bis(4-chlorophenylphosphinyl)]phthalazine. If methylethyl-o-tolylphosphinite is used, the product will be1,4-bis(ethyl-o-tolylphosphinyl)phthalazine. If methyldiisopropylphosphinite is used, the product will be1,4-bis(diisopropylphosphinyl)phthalazine.

EXAMPLE 8 4,6-Bis(dicyclohexylphosphinyl)-2-methylthiopyrimidine

A mixture of 2.50 g of methyl dicyclohexylphosphinite and 1.00 g of4,6-dichloro-2-methylthiopyrimidine in 20 ml of o-dichlorobenzene wasrefluxed under nitrogen for 6.5 hours. Volatiles were removed from themixture under vacuum, and the resulting oily residue was recrystallizedtwice from cyclohexane with decolorizing charcoal treatment and dried at100° C./0.1 mm (13 Pa) to give 0.15 g of4,6-bis(dicyclohexylphosphinyl)-2-methylthiopyrimidine as whitecrystals, mp 197°-198.5° C. Anal. Calcd for C₂₉ H₄₈ N₂ O₂ P₂ S: C,63.25; H, 8.79; N, 5.07; S, 5.82. Found: C, 63.19; H, 8.81; N, 4.89; S,6.04.

If methyl dicyclopentylphosphinite is used in place of methyldicyclohexylphosphinite in substantially the same aforesaid procedure,the product will be4,6-bis(dicyclopentylphosphinyl)-2-methylthiopyrimidine.

EXAMPLE 9 3,6-Bis(diphenylphosphinyl)pyridazine

To a stirred, refluxing solution of 3.00 g of 3,6-dichloropyridazine in50 ml of o-dichlorobenzene under nitrogen was added dropwise 10.00 g ofmethyl diphenylphosphinite. After the addition was completed, themixture was refluxed for 7 hours and then cooled. The cooled mixture wasmixed with excess hexane; the oil which formed slowly crystallized. Theresultant solid was separated by filtration, washed with hexane, andrecrystallized twice from ethanol with decolorizing charcoal treatmentto give 0.93 g of 3,6-bis(diphenylphosphinyl)pyridazine (shown byformula in claim 7) as slightly off-white crystals, mp 248°-251.5° C.Anal. Calcd for C₂₈ H₂₂ N₂ O₂ P₂ : C, 70.00; H, 4.62; N, 5.83; P, 12.89.Found: C, 69.72; H, 4.92; N, 5.78; P, 12.82.

If 3-chloro-6-ethylpyridazine is used in place of 3,6-dichloropyradizinein substantially the same aforesaid procedure of this example, theproduct will be 3-diphenylphosphinyl-6-ethylpyridazine. If3,6-dichloro-4-methylpyridazine is used, the product will be3,6-bis(diphenylphosphinyl)-4-methylpyridazine. If3,6-dichloro-4,5-dimethylpyridazine is used,3,6-bis(diphenylphosphinyl)-4,5-dimethylpyridazine will be the product.

EXAMPLE 10 4-Chloro-6-dimethylphosphinyl-2-methylthiopyrimidine

To a stirred solution of 3.84 g of dimethylphosphinous chloride in 50 mlof degassed dry toluene under nitrogen was added 10.00 g of thallousethoxide. The mixture was stirred for 2 hours and filtered, and to thefiltrate was added 3.25 g of 4,6-dichloro-2-methylthiopyrimidine. Themixture was heated to boiling and cooled to room temperature five timesand then stirred overnight. The mixture was filtered, and the filtratewas evaporated under vacuum. The residue partially crystallized onstanding. The solid was separated and recrystallized from 10 ml oftoluene to give 0.40 g of4-chloro-6-dimethylphosphinyl-2-methylthiopyrimidine as a light-yellowsolid, mp 172°-182° C. with decomposition. Anal. Calcd for C₇ H₁₀ ClNOPS: C, 35.53; H, 4.26; N, 11.84. Found: C, 35.30, 35.17; H, 4.53, 4.44;N, 11.44, 11.58.

If 4,6-dibromo-2-methylthiopyrimidine is used instead of the4,6-dichloro compound in substantially the same aforesaid procedure ofthis example, 4-bromo-6-dimethylphosphinyl-2-methylthiopyrimidine willbe formed.

BEST MODE FOR CARRYING OUT THE INVENTION

The most preferred phosphine oxide, that is, one having three phosphinylgroups, can be prepared by the procedure generally disclosed hereinaboveas being the best method based on my experience and more specificallydisclosed in the examples.

INDUSTRIAL APPLICABILITY

The phosphine oxide of the invention is useful as a flame retardant forpolymeric materials, particularly polyesters and polyamides. Suchmaterials are commonly employed in the textile industry.

We claim:
 1. Phosphine oxide of the formula selected from the group consisting of ##STR11## wherein Y is H, alkyl of 1-4 carbon atoms, Cl, Br, or ##STR12## each of A and A' is selected independently from H and alkyl of 1-4 carbon atoms, or A and A' taken jointly is CH═CH--CH═CH;each of D and D' is selected independently from H and CN, or D and D' taken jointly is CH═CH--CH═CH; and each R is selected independently from alkyl of 1-4 carbon atoms, cycloalkyl of 5-6 carbon atoms, benzyl, phenyl, tolyl, and chlorophenyl.
 2. Phosphine oxide of claim 1 of the formula ##STR13##
 3. Phosphine oxide of claim 1 of the formula ##STR14##
 4. Phosphine oxide of claim 2 of the formula ##STR15##
 5. Phosphine oxide of claim 2 of the formula ##STR16##
 6. Phosphine oxide of claim 3 of the formula ##STR17##
 7. Phosphine oxide of claim 3 of the formula ##STR18##
 8. Polymer having incorporated therein a flame-retarding amount of the phosphine oxide of claim
 1. 9. Polyester having incorporated therein a flame-retarding amount of the phosphine oxide of claim
 1. 10. Polyamide having incorporated therein a flame-retarding amount of the phosphine oxide of claim
 1. 